Acoustic frontend modules

Summary form only given. In the last few years a significant trend towards cellular phones from single band to multi band applications has been observed, especially evident for GSM based devices. About five years ago, there were only a few models offering more than one frequency band of operation. Today, they have been fully substituted by dual-band phones for low-end applications, while triple-band (TB) handsets, previously reserved for the high-end market only, are becoming more and more standard. Due to the increased usage of GSM 850 in the USA there are already a few quad-band GSM phones introduced into the market. Adding third generation services to the existing second generation phones will lead to even more complex antenna interfaces covering 5 to 7 frequency bands for the operation of the mobile phone part plus additional broadband communication like WLAN in the same handheld device. This continuing move towards higher functionality and increased complexity of the antenna interface is in contradiction to the requirements for smaller size, shorter development cycles as well as cost and component count reduction. As passive components outnumber active components these objectives can only be met by a higher level of integration of passive components. Whereas the digital part is already highly integrated, the RF front-end section consists of a large number of passive and active components assembled on a printed circuit board (PCB). In a first step of integration of the antenna interface starting at the end of the 1990\´s the switching between different bands and modes was accomplished by antenna switch modules (ASM). About two years ago higher integrated front-end modules (FEM), based on a combination of the surface acoustic wave receive filters (SAW filters) and a larger number of matching elements together with the ASM, have started to replace these ASMs. LTCC technology (low temperature co-fired ceramics) is the by far most commonly used substrate for these - acoustic" front-end modules. Compared to FR4 or laminates, LTCC is a low loss, high precision substrate allowing to integrate a large number of passive devices in a small volume, e.g., diplexers separating the 1 GHz and 2 GHz frequency bands can be implemented in LTCC with minimum size.